Rupture Cutters with High Penetration Utility

ABSTRACT

A cutting element design that includes a base portion designed to be brazed, pressed or otherwise attached into a drill bit or reaming tool where the design of the cutting element is such that forward drilling force is concentrated in a small area to improve piercement of and/or impingement into the rock to enhance shear and rupture when the element is rotated into the rock on a drill bit. The cutting element is further enabled by the use of a thick, unitary hardened surface coating on an everted working surface to dissipate heat.

FIELD

This invention relates generally to cutting elements used in drill bits in the oil, gas and mining industries having fixed cutters or inserts with ultrahard cutting surfaces and edges made from materials such as diamond, polycrystalline diamond (PDC) or other ultrahard material bonded to or built with an attaching substrate portion, and particularly to fixed cutters or inserts in which the working surface of the cutting element is designed to comprise a small area of impingement or piercement into the rock to enhance shear and rupture when the cutter or insert is rotated into the rock on a drill bit.

BACKGROUND OF THE INVENTION

Rotary drill bits with no rotating or otherwise moving components are typically referred to as “drag” bits or “fixed cutter” bits. These drill bits utilize cutters (sometimes referred to as cutter elements, cutting elements, inserts or compacts) attached to the bit body, with the bit body essentially serving as the carrier for the cutters. Traditionally, these cutters are made of cemented carbide (ex. tungsten carbide) and an ultrahard cutting surface made of polycrystalline diamond material, often referred to as the “diamond layer” or “diamond table” or “working surface,” that is bonded to the cemented carbide substrate at an interface surface.

There are thousands of examples of this type rotary drill bits in existence today. A typical cutter, shown in FIG. 1, is formed of a cylindrical cemented tungsten carbide substrate body with a cemented carbide end used for attachment to the bit body and the opposite end having an engineered surface or interface for attachment of the ultrahard diamond material. The engineered interface serves as attachment point for the ultrahard diamond (or other) material and said ultrahard material forms the working surface with an edge for cutting material. The working surface can be planar, but may likewise have curved exposed surfaces. The diamond layer or working surface meets the side surface of the cylinder to form a cutting edge. FIG. 2 shows a typical drag bit configuration used today in which a conventional cylindrical or round cutter engages a rock formation parallel or approximately parallel to the direction of rotation of the drill bit and shears rock during operation.

In mining for oil and gas and other subterranean materials where drilling a borehole is preferred, it is common for fixed cutter bits to utilize polycrystalline diamond built on the substrate of cemented tungsten carbide to form a polycrystalline diamond compact (PDC) (with the cutters then typically known as PDC cutters, PDC inserts or PDC cutting elements). Drill bits made using such PDC cutters are referred to generally as PDC bits. The carbide substrate cylinder is typically long enough to serve as a mounting means when brazed or otherwise cemented into a corresponding recess or “pocket” on the drill bit body. Primarily, PDC cutter designs are predicated on shear. The drilling of rock involves dragging or forcing the PDC cutter along the bottom of the wellbore hole to induce shearing of the rock. There have been many and various ways to induce and/or improve this shearing effect in PDC cutter design, including chamfers, back rake angles and stylized shapes. The majority of these methods presume the longitudinal axis of the cutter must be oriented generally parallel to the direction of rotation, but with a backrake angle of less than 30 degrees relative to the direction of rotation of the drill bit.

In harder rock, the shape of typical cutters causes the drill bit in which they are mounted to become less responsive to drilling weight due to their predominantly dull shapes relative to the vertical force component of drilling in a well. Much work has been done in the field to improve the ability of conventional cutters to drill through harder rock, with much of this effort directed toward modifications to the back rake and side rake angles at which the cutters are affixed to the drill bit. While improvements have been made, there are fundamental limits as to the extent to which improvements can be made. Both back rake and side rake for PDC cutters dramatically affect force balances in a bit. However, the depth of cut (or penetrating force) directly reflects the loading of each cutter and the magnitude of the forces. Those practiced in the art know that higher back rake angles and side rake angles decrease shearing efficiency, and thus penetration rate. By the same token, extremely low back rake angles (less than 10-12 degrees negative inclination) are problematic for depth of cut, as the substrate carrying the PDC working surface can contact formation and increase torque and drag.

Positive back rake designs can be extremely aggressive, very difficult to control on a drill string and very susceptible to breakage due to loss of supporting carbide—and due to this are rarely used. This fragility exists because the penetrating force exceeds the structural limits of a very pointed cutter whose primary axis is more horizontal than vertical—in other words, the angle of the working surface and the supporting substrate are primarily aligned with drag (shear) force rather than penetrating force (vertical).

In most rock types, the primary alignment of PDC cutters is roughly parallel to the direction of rotation, and utilizes negative back rake angles of up to 30 degrees. Larger back rake angles than this causes the cutters to tend to ride up out of denser rock. This is due to insufficient penetrating force—the rounded cutters have low penetrating force relative to the rock hardness, and thus require the addition of more drilling weight (vertical load or force) to compensate for the harder rock. Typically, the harder rock requires the addition of more cutters due to accelerated wear factors, and the additional cutters lessen the amount of penetrating force per cutter, decreasing drilling efficiency. This is the typical engineering tradeoff seen in design—more cutters make the bit more durable, but decrease individual cutter efficiency. The addition of negative back rake makes the cutters tougher, but decreases shearing efficiency.

The primary focus has been to shear formation, not to penetrate it. This is clearly seen in the prior art. It is a critical function of cutter design to optimize the interaction between the cutter and the rock to balance the competing interests of the removal of rock while maintaining stability of and minimizing vibration within the drill string. An inartfully designed and overly aggressive cutter (one which shears too much rock) may shorten the lifespan of the drillstring. At the other extreme, a cutter which minimizes piercement so as to protect stability will have a rate of penetration too low to be cost effective. Much of the prior an concerning cutter design has sought to optimize this need to balance competing needs, with less than optimal results. However, in general, drill bit design typically incorporates only one type of cutter, which is then mounted in the drill bit so as to accomplish both shearing and piercement tasks. Improvements have been made. For example, U.S. Pat. No. 78,962,106 teaches the use of a pilot cutter to “clear the path” for the primary cutter in a bit. However, the cutter used as a pilot cutter is still round and cylindrical in design. It is merely of a reduced diameter relative to the following cutters. The high cost of drilling mandates the need for additional improvements in drill bit design.

The difficulties in optimizing PDC cutter designs for use in harder rock are manifold. Certainly, harder rock requires a higher vertical load for penetration. Conventional PDC designs are ill suited for penetration, owing to their generally planar shape and limits as to the back rake angles at which they can be disposed. Further, conventional PDC cutter use in a drag bit is optimized for shearing, with only some portion of the forces optimized for penetration. Modification of the design typically finds that as the back rake angle is increased, conventional PDC cutters merely ride up out of the rock rather than penetrate it. To off-set this, additional weight is added to the bit, resulting in a need for additional energy to be put into the drill string and potentially causing addition vibration and other negative effects to the drill string. Further, harder rock formations are commonly dealt with by adding additional cutters to the bit. This, however, reduces the effectiveness of any individual cutter in the bit.

Conventional wisdom likewise looks to modifications of the back rake and/or side rake angles of the cutters placed in a drill bit in order to optimize penetration of the cutters individually and for the bit as a whole. Variations in either of these components can increase or decrease shearing and penetration of individual cutters. At the same time, variations of these can dramatically affect force balances in a bit, potentially leading to dramatically decreased drilling efficiency.

There have been efforts to improve penetration force imparted by drag bits through the use of conical or similarly shaped cutters, such as in US 20120234610 and its counterpart US 20120205163. However, these inventions use one or more conical cutters in combination with planar cutters. Although a variety of cutter designs are mentioned, true optimization of cutter designs is not described in those applications or other publications. Further, prior efforts in this field do not adequately deal with heat associated with harder rock formations. A void exists in the art for cutter designs which optimize the cutters primarily as a means for improving penetration.

A need exist for cutter designs which improve the penetration forces of said cutters in harder rock. A further need exists for a method of placing said improved cutters in drill bits which both shear and penetrate. A further need exists for cutter designs which are optimized more for penetration than for shear or drag forces, while allowing both penetration and shearing. A further need exists for cutter designs and placement which optimize the penetration forces of a drill bits on which said cutters are used without a requirement for additional weight on bit or an increase in cutter density. A further need exists for a PDC cutter with an increased surface area suitable for dissipating the heat generated by drilling through denser and/or harder rock types than is available in conventional planar or semi-planar PDC cutter designs. A further need exists for cutters suitable to be used in combination with conventional planar or semi-planar cutter to improve penetration and shearing.

SUMMARY OF THE INVENTION

It should be regarded that while the present invention is described in general relative to oil and gas well drilling and mining operations, the invention is not limited thereto. The present invention may be practiced in any application in which piercement of rock formation is sought to be optimized as to both rate of penetration and drill string stability and in which shearing of rock formation is undertaken. Further, while representative and exemplary descriptions of penetrating cutting elements are described herein, it should be regarded that penetrating cutter designs are not limited to the disclosed cutting elements, but may be practiced in any application using an everted, three-dimensional cutting element comprising as well a thick, unitary, everted PDC or similar coatings.

The shortcomings of typical drill bit designs, which typically use a plurality of planar or semi-planar cutting elements disposed in an arcing pattern across the face of a drill bit and positioned such that during operation the plurality of planar or semi-planar cutting elements shear some amount of the rock formation away, indicate the need for the present invention. Although the weight of a drill string typically results in sufficient penetration by each of the cutting elements to allow some level of shearing, the design of the standard PDC cutter, being planar, results in shearing not because the cutter is able to cut into the rock formation but simply because the weight of the drill string causes some amount of the cutter to contact the rock formation, the rotational motion of which as part of the drill bit results in some level of shearing of rock formation during operation.

Certainly, it should be considered then that while conventional PDC cutters primarily shear rock, at the same time these cutters also penetrate rock. The design of conventional cutters combined with limitations thereof as to back rake angles suitable for use therewith, do not allow for the optimization of shearing AND penetration. Shearing optimization may be accomplished OR penetration optimization may be accomplished, but not both. This applies as well to conical cutters. While conical cutters are useful for penetration, they also may be used to shear rock. It has not, however, been accomplished in the field where conical cutters have been designed to optimize both shearing and penetration. It is, of course, noteworthy that roller cone drill bit designs typically incorporate penetration as a primary means of rock failure. However, the significant differences between drag bits and roller cone bits known to those skilled in the art teach against the applicability of roller cone methodology to the present invention.

It is not feasible to counter the limitations of typical PDC cutters merely by substituting cutters capable of piercing the rock formation more effectively. Cutters capable of piercing the rock formation too substantially are subject to breaking. Either the individual cutters may break or the shock and vibration induced in the drill string during operation by aggressive cutters may cause other elements of the drill string to fail.

The present invention seeks to balance the competing needs of penetrating rock so as to rupture the rock formation effectively while shearing away other parts of the rock formation, with the overall benefit of improved rate of penetration that does not increase the risk of damage to the drill string.

A primary aspect of the invention is the development of cutting elements suitable for optimized piercement of a rock formation. Therein, cutting elements are designed with a substrate for mounting in a drill bit. A working surface on each cutting element, distal to the mounting substrate, is evened. In addition, each cutter is tapered along a projection on the cutting element distal to the mounting base, such that the diameter of the cutting element where it contacts the rock formation may be 90% or more smaller than the diameter of said cutting element at the mounting base, with a range of reduction of 60%(to 99% useful to this effort. Referring to FIG. 8, testing on exemplary cutters so tapered indicated an increase in the effective penetration force of approximately 20% for less tapered cutters and over 200% for more tapered cutters compared to standard cutters.

Further, in use, whereas the typical planar or semi-planar cutting element for a drill bit is mounted such that the longitudinal axis of the typical planar or semi-planar cutting element is approximately perpendicular to the longitudinal axis of the drill bit, the placement of the cutting element suitable for piercing is made such that the longitudinal axis of the piercing cutting element is parallel or approximately parallel to the longitudinal axis of the drill bit. Whereas the back rake angle of a conventional cutter is limited to a negative back rake angle of less than 30 degrees, a penetrating cutter described herein will be mounted with a substantially higher back rake angle. Further, prior art in the field is substantially limited to conical shapes. Although other shapes for cutting surfaces have been mentioned, sufficient specificity so as to allow significant optimization has not been accomplished. The present invention optimizes the cutting surface designed to optimize penetration so as to augment shearing. The parallel or approximately parallel placement of the cutting element suitable for piercement is undertaken such that the said piercing cutting elements extend into the rock formation, that is, beyond the extent of the shearing cutting elements. Combined with the tapered design of the piercing cutting element, each said piercing cutting element ruptures the rock formation, resulting in more effective shearing of the rock when contacted by the shearing cutting elements.

A plurality of piercing cutters are set into the drill bit in conjunction with a plurality of typical planar or semi-planar cutting elements. In this way, rock formation proximal to the piercing cutters will be ruptured to the extent indicated by the placement of the plurality of piercing cutters relative to the planar or semi-planar cutters. Rupture by the piercing elements results from the weight of the drill string on the rock formation, resulting in a higher rate of rock removal without a need to provide additional force to the drill bit.

Referring to FIG. 3A, a preferred embodiment of the invention is shown in which a cylindrical solid suitable of use as a mounting base comprises an everted, approximately hemispherical working surface distal to the mounting base. A projection proximal to the working surface is disposed on the working surface. Said projection is directed toward reducing the contact area of the cutter against the rock formation, with said projection likewise optimized to improve penetration by fracturing or rupturing the rock in the vicinity of the projection. The working surface and projection are coated with a hardened surface of a unitary structure, typically PDC. The hardened surface effectively dissipates heat associated with drilling through harder rock formations by the combination of its unitary structure, everted (3-dimensional) characteristics and associated increase in unused or unengaged surface area relative to the portion of the cutter engaged in rupturing rock.

Although the cutter of FIG. 3A may be disposed such that its longitudinal axis is parallel to the longitudinal axis of the drill string, the invention may be practiced in embodiments using large angle back rake and side rake angles. Such alternate embodiments are useful in enabling said cutter to shear formation as well as to penetrate formation, and to facilitate mounting of the cutter in an advantageous position within the bit body.

Additional alternative embodiments of the invention allow variations on the shape of the tapered working surface, with embodiments including plows, chisels, teardrops and extra-planar variations of standard PDC cutters. It is noted that in each such alternative embodiment, a thick, unitary, everted PDC or similar coating is employed to dissipate heat efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a perspective view of a planar PDC cutter commonly known in the art.

FIG. 2 depicts a side view of a different planar PDC cutter in which the longitudinal axis of the PDC cutter is approximately perpendicular to the longitudinal axis of the drill bit in which is it mounted. In this position, the PDC cutter is further shown shearing rock formation proximal to the cutting surface of the PDC cutter.

FIG. 3A depicts a perspective view of a piercing cutter in which a narrow projection is disposed on a hemispheric working surface of the cutter.

FIG. 3B depicts a front view of the position of the cutter of FIG. 3A relative to standard cutters in a standard drill bit.

FIG. 4A depicts a side view of an alternate embodiment of the invention in which the shape of the working surface comprises a teardrop shape.

FIG. 4B depicts a from view of the position of the cutter of FIG. 4A relative to standard cutters in a standard drill bit.

FIG. 5 depicts a side view of an alternative embodiment of the intention in which the shape of the working surface comprises an oblique chisel shape.

FIG. 6 depicts a side view of an alternative embodiment of the invention in which the shape of the working surface comprises a centered, tapered chisel.

FIG. 7 depicts a side view of an alternative embodiment of the invention in which the shape of the working surface comprises a plow.

FIG. 8 depicts the results of testing showing the penetration forces imparting by exemplary types of penetrating cutting elements described herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The physics behind the operation of shearing PDC cutters mounted into a drill bit for oil and gas well drilling operations are substantially well known. The hardness of rock formations generally precludes the use of any drill bit or cutter capable of removing a significant amount of rock during any one pass of the cutter. Removing large amounts of rock would require a substantially higher expenditure of energy as well as the introduction of vibration and shock certain to damage the drill string.

FIG. 1 depicts a standard PDC cutter known in the art. The body of the cutter (10) may be cylindrical or similarly shaped. In this representative example, the mounting base of the cutter (11) is planar distal to the cutting surface (12). Distal to the mounting base (11) is the hardened cutting surface (12) made of PDC or another similarly hard material. The longitudinal axis of the cutter is represented (14). While the cutting surface (12) is presented as planar, various non-planar surfaces are known in the art and are not further described herein.

FIG. 2 depicts a representative use of the standard PDC cutter of FIG. 1. The PDC cutter (10) may be braised, cemented or otherwise fixedly attached to a suitable receptacle (26) on a drill bit (25). Although variations are permitted, it is seen that the longitudinal axis of the PDC cutter (14) is substantially perpendicular to the longitudinal axis of the drill bit (27). Variations in the positioning of conventional cutters, primarily as to alternative back rake and/or side rake angles at which conventional cutters may be disposed, are limited such that an overly aggressive rake angle may substantially reduce the effectiveness of the cutter and bit.

Still referring to FIG. 2, during operation, the hardened cutting surface (12) engages the rock formation (28) causing shearing of the rock formation. The extent of the shearing is due primarily to the rate of rotation of the drill bit and the weight of the drill string on each of the cutting elements in the bit, causing each said cutting element to be forced into the rock formation. Although some level of penetration into the rock is effected by the cutter, the primary force of the cutter exerted against the rock is shearing.

In order to operate effectively, PDC drill bits use a large number of PDC cutters, each of which PDC cutters are mounted to cause the shearing of a small amount of rock. The weight of the drill string (the “vertical load”) forces each of the cutters a small distance into the rock, with shearing caused by each as the drill bit is rotated. Penetration is determined by the size of the cutters, the geometry of their placement in the drill bit and vertical load on the cutters, among other things. The appropriate weight of the drill string and the size of the cutters to be used is determined by the hardness of the rock formation through which the drilling is to be undertaken. A general comparison may be made to the difference in saw blades used to cut metal compared to blades used to cut wood. Whereas the teeth of a saw used for cutting wood may be large, so as to remove a substantially larger amount of the softer (compared to metal) wood during each pass of the saw blade, the teeth of a saw blade suitable for cutting the harder metal must be smaller. Large teeth attempting to cut metal would require a significant amount of energy input in order to operate in proximity to a hard material to be cut, would induce a significant level of vibration and would be susceptible to damage owing to the energy necessary to remove bits of metal during operation.

An effective PDC drill bit known in the art balances the effectiveness of the shearing and penetration caused by the PDC cutting elements therein against the energy input needed for operation as well as vibration and shock limits on the drill string in order to maximize its rate of penetration in a cost-effective way.

It is known in the art that care must be taken to prevent the PDC cutters from shearing too much material at a time or from penetrating too deeply into the rock, otherwise damage to the cutter, drill bit or drill string may result. However, this does not mandate that no efforts can be taken to pierce the rock formation more deeply. Logically, if it were possible to concentrate the vertical force component into a smaller area, the ‘piercement’ force values will be higher than a drill bit using traditional components optimized for shear alone. An obvious analogy can be made to forcing a round or blunted object into a block of chalk versus a sharp pointed object. A sharp point penetrates the chalk block deeper than the rounded or blunted object when identical force is applied.

In a preferred embodiment, FIG. 3A depicts a perspective view of a cutting element designed to improve piercement. A cylindrical solid comprises a mounting base (31) distal to an everted hemispherical or approximately hemispherical working surface (32). In this preferred embodiment, a projection (33) is provided proximal to the working surface (32), with the entire surface of the working surface (32) and projection (33) coated with a hardened surface, generally PDC or a similar material. The longitudinal axis of the piercing cutting element is depicted (34).

The design of the piercing cutting element is directed primarily toward engineering the contact area of the piercing cutting element in contact with the rock formation to an area substantially smaller than the cross-sectional area of the mounting base and to a shape other than rounded, dullish shape of typical PDC cutters. Generally, a tapering of the working surface 60-99% smaller than the cross-sectional area of the mounting base is provided. The projection (32) is tapered so as to focus and concentrate the vertical load imparted by each such piercing cutting element into an area small enough to rupture the rock formation by weight alone. Further, the design of the cutter where it engages the formation is fully three dimensional, especially as compared to planar or semi-planar cutters.

Further, the construction of the piercing cutting element includes substantially more diamond surface area than traditional round cutters. This is created to more effectively cool the cutters due to the increased loading they experience when used as primary piercing elements in a drag bit. The load concentration is at the tip or forward edge of these cutters, and the diamond layer geometry must include sufficient diamond surface area and total diamond volume to allow for heat transfer and dissipation during drilling operations. Thus the unengaged, non-working surface area relative to the engaged or embedded or contact surface area has a high degree of relevancy to the construction of piercing cutters due to the increased importance of heat transmission and thermal dissipation.

It should be understood that the exact shape of the piercing cutter in FIG. 3A is representative only. For example, whereas the mounting base (31) is shown as having a circular cross-section, an oval or otherwise shaped mounting bases may be made. Likewise, the everted, hemispherical working surface (32) may take other forms, such as conical, pyramidal, frustoconical or the like. Further, the projection (33) may extend further or less than represented in the figure. One essential aspect of the cutting element design is the creation of a tapered structure on a cutting element designed to concentrate the vertical load of the drill string on an area smaller than the cross-section of the mounting base of cutter, with such concentration sufficient to rupture a rock formation thereby and further represented by the inclusion of a unitary PDC or similar coating comprised of a surface area, geometry and thickness to allow effective heat dissipation.

When drilling rock (as in the chalk block analogy), concentrating the vertical forces into a small area focuses rupture forces, allowing deeper penetration into rock. By designing a cutter shape that is primarily directed at piercing into hard rock and secondarily to shear, the vertical drilling forces are better optimized to fail rock, by virtue of having penetrated farther into the rock prior to and during shear induced by rotating the drill bit. In general, in harder rock, a higher piercing force into the formation would be required to initiate rupture during rotation of the drill bit. Nevertheless, the ability of the cutter to shear formation is not reduced to zero. Instead, the design of the invention allows highly effective penetration and rupture of rock formation with a useful level of shear capabilities.

Alternate embodiments of the invention provide for the use of large angle back rake and side rake angles to be used in mounting the tapered cutter in a drill bit. Variation of the rake angles allow additional optimization of the penetration force and shear force exerted by the cutter for formations of different hardnesses.

In an additional alternate embodiment of the cutter of FIG. 3A, the lack of rotational symmetry of the cutter, as particularly noted in FIG. 3A, allows the positioning of the cutter in the bit to enable more or less of the projection (33) to contact the rock, allowing additional variability of the shearing force of the cutter during operation. For example the line of the projection (33) may be set so that it lies parallel to the direction of rotation of the bit, thereby minimizing the extent to which the projection effects a shearing force. Alternatively, the line of the projection (33) may be set perpendicular or at some angle between parallel and perpendicular to the direction of rotation of the bit, increasing the shearing effect of the projection (33) in the rock.

The invention is enabled by the use of a unitary hardened surface on the specific working surface created on the cutter. It is known in the art the ability of hardened surfaces, such as diamond, PDC or the like to dissipate heat effectively. PDC coatings have gained wide acceptance in the field to-date, owing in part to its ability to dissipate heat. It's utility in drag bit designs, in particular, is noted. This compares to conical cutters used in roller cone bits, in which the lower level of heat produced allows the use of materials other than PDC, such as tungsten carbide. The design of the working surface in each embodiment of the invention, in which an everted surface, whether hemispherical, conical or otherwise, with additional working structures, such as the projection (33) provide an increase in the unengaged area of the working surface. Coated with a suitable hardened surface, this additional unengaged working surface area increases the amount of heat which can be dissipated during operation, allowing drilling to be undertaken through harder rock types. Further, the continuous, unitary design of the hardened surface further increases heat dissipation, as opposed to hardened coatings comprised of multiple hardened surface, interfaces, seams or similar contiguous methods, which improve heat transfer and dissipation.

The invention does not require additional drilling energy and actually is more efficient by way of improvement in utilization of existing penetrating forces. As shown in FIG. 8, which will be full fully described below, the Mohawk cutting element described in FIG. 3A imparts a penetration force approximately 20% greater than that imparted by a standard cutter. As such, replacing 50% of the round cutters with penetrating cutters would result in either an increase in penetration rate over a bit without penetrating cutters or a reduction in the vertical force required to achieve a given rate of penetration. Further, if we assume the formation is ruptured at a deeper depth by penetrating further into the rock, then the corresponding deeper and farther extending rupture of formation will also occur, making the remaining rock weaker. This weaker rock can then be addressed with less energy by the traditional rounded PDC cutters that flank, follow or precede the penetrating cutters.

FIG. 3B depicts a front view of the Mohawk cutter depicted in FIG. 3A in position relative to standard planar cutters (30) with which it would be associated in a typical drag bit. As shown in the figure, three circular cutters (30) are placed in different blades of a drag bit, the overlap of their cutting paths being shown in the rotation of the bit. The projection (33) of the cutter of FIG. 3A extends beyond the outer limit of the round cutters (30). In position against a rock formation, the projection (33) would necessarily precede the round cutters (30), rupturing and weakening rock to reduce energy needed for shearing the rock by the round cutters (30). The depth of penetration of the projection (33) may be more or less than shown, depending on characteristics of the formation and other drilling factors.

FIG. 4A depicts an alternative embodiment of the invention, in which a cylindrical solid comprises a mounting base (41) distal to an everted hemispherical or approximately hemispherical working surface (42). A planar surface (43) is produced, formed or otherwise disposed on the working surface, producing a smooth surface in the shape of a teardrop (45). The entire surface of the working surface (42) and smooth surface (45) are coated with a hardened surface. The longitudinal axis of the teardrop cutting element is depicted (44). As with the preferred embodiment, this alternate embodiment allows optimization using various rake angles in mounting as to penetration and shear, depending upon need. Further, as with the preferred embodiment, the large unengaged area of the hardened surface coating allows for effective heat dissipation. Again referring to FIG. 8, testing of the penetration force imparted by the teardrop cutter reflected an increase of penetration forces of approximately 57% over that of the standard cutter.

FIG. 4B depicts a front view of the teardrop cutter depicted in FIG. 4A in position relative to standard planar cutters (40) with which it would be associated in a typical drag bit. As shown in the figure and similarly to FIG. 3B, three circular cutters (40) are placed in different blades of a drag bit, the overlap of their cutting paths being shown in the rotation of the bit. The projection 433) of the cutter of FIG. 4A extends beyond the outer limit of the round cutters (40). In position against a rock formation, the projection (43) would necessarily precede the round cutters (40), rupturing and weakening rock to reduce energy needed for shearing the rock by the round cutters (40). The depth of penetration of the projection (43) may be more or less than shown, depending on characteristics of the formation and other drilling factors. Further, the teardrop cutter of FIG. 4B contains a flat area disposed to face the direction of rotation. This design feature allows the teardrop cutter to both pierce formation and shear simultaneously. This is a very advantageous design aspect when drilling formations that have laminated intervals of alternating soft and hard rock types: an effective hybridization of penetrating and shearing forces.

FIG. 5 depicts an alternative embodiment of the invention, in which a cylindrical solid comprises a mounting base (51) distal to an everted conical working surface (52). Two or more planar surfaces (53) are produced, formed or otherwise disposed on the working surface, producing two or more smooth surfaces in the shape of an oblique chisel (55). The entire surface of the working surface (52) and smooth surfaces (55) are coated with a hardened surface. The longitudinal axis of the oblique chisel cutting element is depicted (54). As with the preferred embodiment, this alternate embodiment allows optimization using various rake angles in mounting as to penetration and shear, depending upon need. Further, as with the preferred embodiment, the large unengaged area of the hardened surface coating allows for effective heat dissipation.

FIG. 6 depicts an alternative embodiment of the invention, in which a cylindrical solid comprises a mounting base (61) distal to an everted conical working surface (62). Two or more planar surfaces (63) are produced, formed or otherwise disposed on the working surface, producing two or more smooth surfaces in the shape of a tapered chisel (65). The entire surface of the working surface (62) and smooth surfaces (65) are coated with a hardened surface. The longitudinal axis of the tapered chisel cutting element is depicted (64). As with the preferred embodiment, this alternate embodiment allows optimization using various rake angles in mounting as to penetration and shear, depending upon need. Further, as with the preferred embodiment, the large unengaged area of the hardened surface coating allows for effective heat dissipation.

FIG. 7 depicts an alternative embodiment of the invention, in which a cylindrical solid comprises a mounting base (71) distal to an everted cylindrical working surface (72). Two or more planar surfaces (73) are produced, formed or otherwise disposed on the working surface, producing two or more smooth surfaces in the shape of an angled plow (75). Alternatively, it is well within the manufacturing capabilities of PDC to manufacture this surface as designed. The entire surface of the working surface (72) and smooth surfaces (75) are coated with a hardened surface. The longitudinal axis of the angled plow cutting element is depicted (74). As with the preferred embodiment, this alternate embodiment allows optimization using various rake angles in mounting as to penetration and shear, depending upon need. Further, as with the preferred embodiment, the large unengaged area of the hardened surface coating allows for effective heat dissipation. Again referring to FIG. 8, testing of the plow cutting element as to penetration force imparted indicted an increase in said force of approximately 240% over that imparted by a standard cutter.

FIG. 8 depicts graphically the results of testing of the penetration forces of different types of exemplary cutting elements. Each of the cutting element types were tested by applying 714 pounds of vertical load to each cutting element. Penetration forces in pounds per square inch were then directly measured. For this testing, cutting element shapes were made from hardened steel and brass was used to simulate the rock due to its relative softness. In actual production, hard and ultra-hard base metals are used as well as ultra-hard surface coatings to assure longevity. 

1) A method of improving drilling rates for oil and gas borehole drilling in which tapered cutting elements are substituted for one or more standard cutting elements, and in which said tapered cutting elements are designed to improve the penetration forces into rock formation by at least 20% over standard cutter designs. 2) The method of claim 1 in which the use of one or more tapered cutting elements allows the reduction of weight on bit with little or no loss of cutting efficiency. 3) The method of claim 1 in which the use of one or more tapered cutting elements allows a higher rate of drill bit penetration with little or no loss of drill bit stability. 4) A fixed cutter for earth drilling and boring, the cutter comprising: a substrate end for mounting in a drill bit or reaming tool, said substrate having a periphery, an end surface and a longitudinal axis extending through said end surface; and an everted, non-planar working surface opposite the mounting end which contains a shape that is reduced in diameter relative to the mounting end by at least 20%, and designed primarily to concentrate any force applied to the mounting end, via the longitudinal axis, to a smaller area relative to the mounting end; said working surface is disposed with a circumferential ultra hard material layer, wherein the ultra hard material layer is applied or disposed such that it forms a surface more than degrees in circumference on the periphery relative to the longitudinal axis. 5) The cutting element of claim 4 in which the penetration forces imparted by said cutting element is at least 20% greater than the penetration forces imparted by a standard cutter known in the industry. 6) The cutting element of claim 4 in which said cutter is positioned such that it is the primary penetrating element into the rock formation when the drill bit is lowered to the bottom of the hole, concentrating the bit drilling weight into highly focused areas prior to initiation of rotational forces and shearing of the rock. 7) The cutting element of claim 4 in which said cutter positioned in offset position relative to traditional planar working surface cutters and semi-planar working surface cutters to initiate rupture of the desired rock to weaken it prior to the traditional shearing effect seen with planar and semi-planar cutters. 8) The cutting element of claim 4, in which the everted surface coating of the cutting element effectively dissipates heat from the cutting element during drilling operations. 